There is considerable interest in developing an inorganic foundry binder which has the performance characteristics of commercial organic foundry binders. Organic foundry binders, particularly those based upon polyurethane chemistry, have been used in the casting industry for several decades in both the no-bake and cold-box processes. This is because they produce foundry molds and cores with acceptable tensile strengths that shakeout of castings with relative ease. The castings prepared with these foundry molds and cores have a good surface finish with only minor defects.
Currently, the effects of organic foundry binders on the environment and health are under study. Consequently, there is an interest in considering alternative binders in case these studies are negative. Inorganic foundry binders are of particular interest because they are not subject to some of the concerns associated with organic foundry binders.
Various compositions of inorganic foundry binders are known. See for example U.S. Pat. No. 3,930,872 which describes an inorganic foundry binder comprising boronated aluminum phosphate and an oxygen-containing alkaline earth metal in specified amounts. Although these binders produce molds and cores that have adequate strength and shakeout easily from metal castings prepared with them, the binders exhibit high viscosity, are not very flowable and are not well suited for use with continuous mixers. Furthermore, molds and cores prepared with these binders do not exhibit adequate humidity resistance.
As another example of an inorganic foundry binder, see U.S. Pat. No. 4,111,705 which describes an inorganic no-bake foundry binder comprising orthophosphoric acid, a ferrous oxide containing material, and a water-soluble alkali metal or ammonium salt of certain carboxylic acids. U.S. Pat. No. 4,430,441, also describes a no-bake inorganic foundry binder comprising from 95-99 weight percent of a refractory filler containing magnesium oxides, iron oxides, silicon oxides or mixtures thereof and from 1 to 5 weight percent of an organic acid having a specified dissociation constant.
The binders disclosed in the latter two patents are not practical to use on a commercial scale. They do not produce foundry molds and cores with adequate strengths that easily shakeout of the castings prepared with them, and the castings produced are not substantially free of major defects. Furthermore, the work time and the strip time of the molds and cores produced with these binders are not acceptable from a commercial perspective.